Of all the dangerous government surveillance powers that were expanded by the USA PATRIOT Act the National Security Letter (NSL) power under 18 U.S.C. § 2709 as expanded by PATRIOT Section 505 is one of the most frightening and invasive. These letters served on communications service providers like phone companies and ISPs allow the FBI to secretly demand data about ordinary American citizens’ private communications and Internet activity without any meaningful oversight or prior judicial review. Recipients of NSLs are subject to a gag order that forbids them from ever revealing the letters’ existence to their coworkers to their friends or even to their family members much less the public. (source)